Field of the Invention
The invention relates generally to the art of axle/suspension systems for heavy-duty vehicles. More particularly, the invention relates to air-ride axle/suspension systems for heavy-duty vehicles, which utilize an air spring to cushion the ride of the vehicle. More specifically, the invention is directed to the conversion of a non-damping air spring to an air spring with damping characteristics, which is accomplished by sealing the non-damping air spring piston to create a piston chamber and providing fluid communication between the piston chamber and a bellows chamber of the air spring in order to provide damping characteristics to the air spring.
Background Art
The use of one or more air-ride trailing and leading arm rigid beam-type axle/suspension systems has been popular in the heavy-duty truck and tractor-trailer industry for many years. Although such axle/suspension systems can be found in widely varying structural forms, in general their structure is similar in that each system typically includes a pair of suspension assemblies. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to main members, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle axle/suspension systems suspended from main members of: primary frames, movable subframes and non-movable subframes.
Specifically, each suspension assembly of an axle/suspension system includes a longitudinally extending elongated beam. Each beam typically is located adjacent to and below a respective one of a pair of spaced-apart longitudinally extending main members and one or more cross members, which form the frame of the vehicle. More specifically, each beam is pivotally connected at one of its ends to a hanger, which in turn is attached to and depends from a respective one of the main members of the vehicle. An axle extends transversely between and typically is connected by some means to the beams of the pair of suspension assemblies at a selected location from about the mid-point of each beam to the end of the beam opposite from its pivotal connection end. The opposite end of each beam also is connected to an air spring, or its equivalent, either directly or via a pedestal, and the air spring is in turn connected to a respective one of the main members. The air spring cushions the ride of the axle/suspension system during operation and, in some cases, provides damping characteristics. In those cases where the air spring does not provide damping, one or more shock absorbers are employed to provide damping. A height control valve is mounted on the hanger or other support structure and is operatively connected to the beam and to the air spring in order to maintain the ride height of the vehicle. A brake system is also included on the vehicle axle/suspension system. The beam may extend rearwardly or frontwardly from the pivotal connection relative to the front of the vehicle, thus defining what are typically referred to as trailing arm or leading arm axle/suspension systems, respectively. However, for purposes of the description contained herein, it is understood that the term “trailing arm” will encompass beams which extend either rearwardly or frontwardly with respect to the front end of the vehicle.
The axle/suspension systems of the heavy-duty vehicle act to cushion the ride, dampen vibrations and stabilize the vehicle. More particularly, as the vehicle is traveling over the road, its wheels encounter road conditions that impart various forces, loads, and/or stresses, collectively referred to herein as forces, to the respective axle on which the wheels are mounted, and in turn, to the suspension assemblies that are connected to and support the axle. In order to minimize the detrimental effect of these forces on the vehicle and/or its cargo as it is operating, the axle/suspension system is designed to react and/or absorb at least some of them.
These forces include vertical forces caused by vertical movement of the wheels as they encounter certain road conditions, fore-aft forces caused by acceleration and deceleration of the vehicle due to operation of the vehicle and/or road conditions, and side-load and torsional forces associated with transverse vehicle movement, such as turning of the vehicle and lane-change maneuvers. In order to address such disparate forces, axle/suspension systems have differing structural requirements. More particularly, it is desirable for an axle/suspension system to minimize the amount of sway experienced by the vehicle and thus provide what is known in the art as roll stability. However, it is also desirable for an axle/suspension system to be relatively flexible to assist in cushioning the vehicle from vertical impacts, and to provide compliance so that the components of the axle/suspension system resist failure, thereby increasing durability of the axle/suspension system. It is also desirable to dampen the vibrations or oscillations that result from such forces in order to reduce wheel and/or suspension bounce, which in turn can potentially harm the wheels and the components of the axle/suspension system, thereby reducing optimal ride characteristics of the axle/suspension system and the life of the components of the axle/suspension system. A key component of the axle/suspension system that cushions the ride of the vehicle from vertical impacts is the air spring or other spring mechanism, such as a coil spring or a leaf spring, while a shock absorber typically provides damping to the axle/suspension system. In some instances, the air spring can also provide damping to the axle/suspension system.
The typical air spring of the type utilized in heavy-duty air-ride axle/suspension systems includes three main components: a flexible bellows, a bellows top plate, and a piston. The bellows is typically formed from rubber or other flexible material, and is sealingly engaged with the bellows top plate and also to the top portion of the piston. The volume of pressurized air, or “air volume”, that is contained within the air spring is a major factor in determining the spring rate of the air spring. More specifically, this air volume is contained within the bellows and, in some cases, the piston of the air spring. Usually, the larger the air volume of the air spring, the lower the spring rate of the air spring. A lower spring rate is generally more desirable in the heavy-duty vehicle industry because it allows for softer ride characteristics for the vehicle. Typically, the piston either contains a hollow cavity, which is in communication with the bellows and which adds to the air volume of the air spring by allowing unrestricted communication of air between the piston and the bellows volumes, or the piston has a generally hollow cylindrical-shape and does not communicate with the bellows volume, whereby the piston does not contribute to the air volume of the air spring. In any event, the air volume of the air spring is in fluid communication with an air source, such as an air supply tank, and also is in fluid communication with the height control valve of the vehicle. The height control valve, by directing air flow into and out of the air spring of the axle/suspension system, helps maintain the desired ride height of the vehicle. Most prior art air springs of the non-damping variety utilize a “molded-in” end closure that is attached to the top plate of the piston by a fastener. In this design, the bottom end of the bellows is integrally molded with a metal end closure, so that the end closure is typically not removable from the bellows. These types of air springs make up a majority of the non-damping air spring market and typically do not exhibit the disadvantages of the “take-apart” design described below.
Prior art air springs such as the one described above, while providing cushioning to the vehicle cargo and occupant(s) during operation of the vehicle, provide little if any damping characteristics to the axle/suspension system. Such damping characteristics are instead typically provided by a pair of hydraulic shock absorbers, although a single shock absorber has also been utilized and is generally well known in the art. Each one of the shock absorbers is mounted on and extends between the beam of a respective one of the suspension assemblies of the axle/suspension system and the hanger mounted on a respective one of the main members of the vehicle. These shock absorbers add complexity and weight to the axle/suspension system. Moreover, because the shock absorbers are a service item of the axle/suspension system that will require maintenance and/or replacement from time to time, they also add additional maintenance and/or replacement costs to the axle/suspension system.
The amount of cargo that a vehicle may carry is governed by local, state, and/or national road and bridge laws. The basic principle behind most road and bridge laws is to limit the maximum load that a vehicle may carry, as well as to limit the maximum load that can be supported by individual axles. As a result, the weight of the shock absorbers undesirably reduces the amount of cargo that can be carried by the heavy-duty vehicle. Depending on the shock absorbers employed, they also add varying degrees of complexity to the axle/suspension system, which is also undesirable.
Because of the undesirable increased weight to the axle/suspension system attributed to the shock absorbers, prior art air springs with damping characteristics were developed. Prior art air springs with damping characteristics enabled removal of the shock absorbers while maintaining desirable soft ride characteristics. More specifically, prior art air springs with damping characteristics typically included openings between the bellows and the piston in order to allow fluid communication between the volume of the bellows chamber and the volume of the piston chamber. This fluid communication between the bellows chamber volume and the piston chamber volume provided damping characteristics to the air spring while maintaining a soft ride to the vehicle during operation. Prior art air springs with damping characteristics are typically of the “take-apart” design variety, meaning that the bottom end of the bellows of the air spring is operatively connected to a protrusion that extends upwardly from the piston top plate that is formed with a barb. In these types of air springs, the bellows can be taken apart from the piston. However, air springs having the “take-apart” design are limited during rebound travel and jounce travel and can experience fold in issues in “low pressure” or “no air” situations.
Although prior art air springs with damping characteristics provide a softer ride during vehicle operation, they typically require a custom designed air spring piston for each specific application. More specifically, each anticipated use of the axle/suspension system requires certain damping characteristics, which, in turn, requires a different air spring configuration. As a result, each prior art air spring with damping characteristics requires a different custom design and manufacturing process. This leads to undesirable increases in both design and manufacturing costs and an undesirable increase in production time for the air spring. Moreover, the “take-apart” design of the air springs with damping characteristics potentially limits rebound travel and jounce travel and potentially exacerbates fold in issues in “low pressure” or “no air” situations. The air spring for heavy-duty vehicles of the present invention overcomes the problems associated with prior art non-damping air springs by removing the prior art shock absorber and converting the non-damping air spring with a “molded-in” end closure into an air spring that provides damping characteristics. It also allows for the use of different piston/pedestal combinations to be used in the air spring so that the volume of the piston can be varied along with the opening size between the piston chamber and the bellows chamber to optimize the damping characteristics of the air spring. Additionally, the air spring for heavy-duty vehicles of the present invention provides an air spring with damping characteristics that may be optimized for different uses without requiring custom design and manufacturing of the air springs for each specific use, as is typically required by prior art air springs with damping characteristics.